This three-year qualitative study entitled, "MDMA and STD/HIV risk among hidden networks of ecstasy-using young adults," will investigate the interaction of ecstasy and sexual risk-taking among vulnerable young adults (ages 18-25) in the Hartford, CT region where STD/HIV rates are highest in the state and MDMA distribution and use are widespread. Aims are: (1) Identify cultural scenarios (contextual conditions, behavioral sequences and explanatory themes) that link MDMA and sexual risk through focus groups with 50 youth in the target population; (2) document the role of MDMA in relation to risky sex through in depth- interviews on drug histories and recent events involving unprotected and protected penetrative sex, with and without MDMA use, with 120 participants (50% male and female, and equally divided by ethnicity (Latino, African American and Euro-American); (3) utilize thematic, Qualitative Comparative Analysis and Ethnographic Decision Modeling to analyze the events and determine the unique contribution of MDMA to unprotected sex and the decision making that results in this outcome; (4) compare cultural scenarios against interpersonal scripts to demonstrate the importance of adding real-life solutions to existing cultural repertoires involving MDMA and sexual risk-taking; and (5) conduct focus groups with youth, service providers, media and other youth cultural opinion leaders, educators and policy makers based on study results to identify multilevel intervention approaches. The study is guided by scripting theory. The unique combination of qualitative analytic methodologies employed in this study addresses problems confronted by quantitative researchers, whose findings have thus far been inconclusive with respect to establishing causal links between substances including alcohol, marijuana and MDMA, and unprotected sex and other sexual risks. Using set theory and Boolean logic, Qualitative Comparative Analysis offers equations that isolate the unique contributions of single drugs such as MDMA to sexual risks in the context of other drug use and other contributing factors. The study also addresses the limitations of scripting studies which assume behavioral patterns based on cultural scenarios and fail to explore the full range of people's lived experience and practices. By doing so, this study promises to find new approaches to preventing the specific circumstances under which MDMA and sexual risk-taking occur. The proposal thus addresses directly the public health concern that MDMA (with and without other drugs) may increase sexual risk behaviors that facilitate transmission of STDs/HIV; it also addresses as yet unsolved methodological problems associated with determining the relationships between substance use and risky sex, which has implications for other public health approaches to this problem.